1. Field of the Invention
The present invention relates generally to the field of rotary power tools. In particular the present invention relates to a tool-free mechanism for gripping interchangeable rotary tool accessories, such as circular saw blades and grinding wheels.
2. Discussion
Various types of rotary power tools require a user to selectively attach a tool accessory, such as a circular saw blade or grinding wheel. Over the course of a particular project or work period it may be necessary to employ a variety of such accessories and to replace worn or broken ones. Convenient removal and replacement of the interchangeable tool accessories is therefore desirable.
Various methods are employed for gripping such accessory discs. For example, in current circular saw designs a blade has a center hole. The hole may be circular or a shape with sides and corners. A diamond shaped hole is well known for some applications. The hole in the blade fits over the end of the saw's output shaft or an extension thereof, with the plane of the blade transverse to the axis of the shaft. For some radial distance the axially inward facing surface of the blade rests against a flat shoulder of the shaft or an inner washer connected to the shaft.
Conventionally, the blade is clamped in place against the shoulder or inner washer with a retaining-nut threaded down over a threaded end of the drive spindle. An outer washer may be placed between the nut and the blade. When changing blades, the nut must be loosened and removed. The tightening and loosening of the nut may be partially performed by hand, but the size and shape of the nut make it difficult and/or uncomfortable to properly tighten and then initially loosen using hands alone. Therefore, it is necessary to use a hand wrench or similar tool in order to apply sufficient torque to the retaining nut.
Additionally, when tightening or loosening the nut, the shaft/spindle must be prevented from rotating or else it would be difficult to achieve relative motion between the nut and the rotatable spindle. Formerly, the loosening and tightening process required that the operator simultaneously grip both the shaft/spindle and the nut with two separate hand wrenches or the like. Then a torque was applied to the nut while the shaft was held in place. This was an awkward process and made even more so by the necessity to support the weight of the tool itself.
More recently, tools have been designed that incorporate a locking mechanism that locks the shaft/spindle relative to the tool housing. Thus, the rotation of the shaft can be prevented, simply by employing the built in shaft lock. For such a power tool, only one hand wrench is required to loosen or tighten the nut.
The need to use even one hand tool to change saw blades or grinding wheels, however, is still inconvenient. For example, when a blade replacement is required, the tool operator has to stop what he is doing to find a wrench, which may not be readily at hand.